The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.
Authentication Score 3
Original Citation
Newton, Isaac. "Axiomata sive Leges Motus: [Axioms, or Laws of Motion]." Philosophiae Naturalis Principia Mathematica [The Mathematical Principles of Natural Philosophy], vol. 1. London: Josephi Streater, 1687, law 2.
Current Citation
Newton, Isaac. "Axioms, or the Laws of Motion." The Principia, translated by Andrew Motte. Prometheus, 1995, law 2.